did you learn the term "hot water tank pop off" in school. haha. so every time your hwt heats up, it has nowhere to expand because of your check valves and it will open your T&P valve. good idea. I've been installing underfloor heating for 20 years and plumbing for a lot more. 99% of houses in our area do not have exp. tanks on hwt's, thers just no need to unless you install check valves. you should sell me some of those recirc pumps with timers for $100, i'll make a fortune. You should get your license revoked if you ever tried what your proposing. My advise to anyone is do it right the first time and save yourself time and money in the end.